Recently, C.sub.4 -C.sub.7 hydrocarbon blowing agents have gained increasing importance as zero ozone depletion potential alternative blowing agents for polyurethane foams. One problem associated with the use of hydrocarbons is their low solubility in polyols and isocyanates. Blowing agent incompatibility with polyols can lead to processing difficulties on high pressure impingement mixing machines, most noticeably with the calibration of the isocyanates/polyol ratio. The publication in the Oct. 10-13th, 1993 issue of Polyurethanes World Congress entitled "Hydrocarbons Provide Zero ODP and Zero GWP Insulation for Household Refrigeration" describes a foaming apparatus adapted for use with the hydrocarbon blowing agents. As can be seen from FIGS. 2 and 3 in the description of this publication, the hydrocarbon is separately metered into the mix head, or fed into a day tank which is kept under constant agitation. Most of the insulation foams use polyester-based polyols as the base polyol, in which hydrocarbons have only a limited or no solubility. Therefore, to avoid phase separation, the hydrocarbon blowing agent is either metered separately into the high pressure mix head, or kept under constant agitation in a day tank immediately prior to being fed to the mixhead.
It would be desirable to avoid adding the hydrocarbon as a third stream to the mixhead. Since hydrocarbons tend to separate from the polyester based polyols within hours, sometimes minutes, after ceasing vigorous mixing, it would be desirable to formulate a polyol composition in which the hydrocarbon blowing agent is solubilized or held in solution without agitation. A hydrocarbon held as a solution in the polyol would have the advantage of a more uniform distribution throughout the polyol.